The present invention relates to a pattern measuring method by using image information of microscope image displayed on a display as in a scanning ion microscope or a scanning electron microscope and a system executing the method.
Measurement of a pattern length using a scanning microscope such as a scanning ion microscope or a scanning electron microscope, can be dealt with as screen coordinate information in an microscope image having a high magnification and therefore, in measuring a distance between two points, in principle, the distance can be detected by accuracy of image resolution. Conventionally, there has widely been carried out length measurement of a submicron order as in a semiconductor pattern by using the technology. According to the method, for example, in measuring a length of a pattern as shown by FIG. 5A, an area is set in an observation image of the microscope by drawing two pieces of cursor lines 40a and 40b in the horizontal direction, brightness information along a plurality of pieces of scanning lines in the area, is summed up in the vertical direction to thereby provide a line profile signal 32 as shown by FIG. 5B to thereby detect edges thereof and measure a distance between the edges. It is general that the edges are detected by calculating positions of maximum inclination of the line profile signal 32, that is, calculating a differentiated signal 33 of the line profile signal 32 and determining the edges by a maximum value and a minimum value thereof as shown in FIG. 5C. Although the method can execute proper measurement when a pattern is constituted by a constant width as in the example, the method is not applicable when the pattern is of an indefinite complicated shape or an angle made by two pieces of nonparallel straight lines or dimensions of an upper side and a bottom side of a trapezoidal shape, is intended to provide.
Conventionally, in measuring a length of a pattern formed by nonparallel lines, there is adopted a method of calculating a distance between two points from screen coordinates by previously determining a portion between two points to be measured such as a width dimension of a front end, a width dimension of a base portion, or a dimension in a longitudinal direction of a pattern from an image of the pattern and plotting to specify corresponding points on an observation image by an operator. According to the method, the distance between the plotted two points can finely be measured in an image resolution order. However, the corresponding points are specified based on pattern recognition of an operator, further, plotting is carried out by manual operation and therefore, even when the length is measured with regard to the same sample, the acquired data is accompanied by a dispersion by individual difference and in respective measurement. For example, when a width of a front end of a pattern formed on a semiconductor device, is measured, corner portions of the pattern are generally formed to be rounded when viewed on an observation image in a procedure of forming the pattern by lithography and therefore, there is not an absolute reference in to which locations positions of both ends of the front end width portion are to be specified. Therefore, specification of the corresponding points is entrusted to the selection based on the determination of the operator at respective time. This causes the dispersion.
It is a problem of the invention to provide a measuring method having high objectivity and reproducibility, which can measure a shape of an arbitrary pattern surrounded by nonparallel lines in measuring the pattern using display image information as a scanning microscope and in which individual difference or an error for respective measurement is difficult to be brought about, further, to provide a system realizing the measuring method.